I suspect many of them will be ERC20 tokens or similar on PoS chains - some will be on current chains , though some will be on their own launched and validated by their own nodes
I expect all of these types can be integrated into DEX's , though I do not think this is what the CBDC people envisage - but cross trading with other CBDCs will have to be possible , which would enable DEXs to add pairs
once the genie is out of the bottle